Issues with the River Ver and Lake

The River Ver is a chalk stream and a tributary of the River Colne in Hertfordshire. Chalk streams are an internationally rare habitat. There are only around 200 worldwide, most of which are in southern England. Chalk streams are defined as watercourses that get most of their flow from chalk-fed groundwater. They should also show the classic chalk stream characteristics of crystal clear water flowing over a clean gravel bed. As their flow comes predominantly from chalk aquifers, they should have stable temperature, pH and flows which rise and fall slowly, reflecting the level of the groundwater.

The River Ver has been historically altered for e.g. milling, flood risk, amenity and recreation. These alterations include:

River Ver

Impoundments

Restrict fish passage

Loss of bed gradient

Excessive bed siltation upstream

Loss of natural habitat and flow diversity upstream

Hard engineering (e.g. concrete banks)

limits the ecology and habitats

Over-wide and straight channel

Lack of flow diversity

Lack of habitat diversity

Excessive bed siltation

Reduced resilience to climatic changes

Realignment of river channel

Perched channel (the river is at a higher level than the valley bottom) resulting in disconnection from the groundwater table which is very important for a chalk stream.

Loss/disruption of bed gradient

Disconnection from flood plain

Reduced resilience to climatic changes

Dredging

Reduced channel habitat and flow diversity

Dredging bunds along the channel restrict floodplain connectivity

Increased groundwater abstraction

Reduces river flows

Increases frequency of low flows/channel drying

Limits river ecology, especially in combination with the other alterations listed

Limits river ecology, especially in combination with the other alterations listed

Such alterations limit the form and processes that create and sustain the habitat to support the ecology within the river. The result is that most of the River Ver through St Albans has lost its chalk stream characteristics and is in a poor condition.

Below are two photographs, the first shows the poor quality of the River Ver through Verulamium Park with silty bed, hard banks, no vegetation and an overly wide channel. The second shows the Ver near Sopwell House which shows a much more representative image of a chalk stream with clean gravel bed suitable for fish to spawn, lush marginal and in-channel vegetation such as the iconic chalk stream plant water crowfoot and natural banks gently sloping down to the water

Issues with Verulamium Park lakes

The lakes in Verulamium Park were constructed between 1929 and 1932 partly to give much needed work to the unemployed during the depression. The lakes were lined with hand poured concrete and are no more than about 1m deep. Some of the issues with the lakes are:

Low throughput of flow

The lakes are fed by the River Ver via a sluice gate into the northern boating lake. The volume of the lakes is comparatively very large to the amount of flow they receive from the River Ver. As we mentioned above, the river itself suffers from low flows and often doesn’t have water to spare for the lakes. When the river level is too low, no water enters the lake.

Eutrophication – the lake is too nutrient rich. Causes of this are:

River water (which feeds the lakes) is naturally more nutrient rich that lake water should be

The lakes have a high surface area to volume ratio making them more susceptible to dramatic water temperature increases in summer. This can create conditions which cause algal blooms and oxygen crashes.

Avian botulism outbreaks

Botulism bacterial spores are naturally occurring and can survive for years. However, the bacteria only produce toxins under particular environmental conditions, which are generally believed to include warm temperatures, anoxic conditions and an organic nutrient source.Poor water quality (water quality analysis is being carried out to provide more detail on this)